This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from the inventor""s application PRINTER AND METHOD OF CONTROLLING THE GAP OF FUSING ROLLER filed with the Korean Industrial Property Office on Feb. 21, 2000 and there duly assigned Serial No. 8180/2000.
1. Field of the Invention
The present invention relates to a printer in which the gap between the transfer roller and the fusing roller is adjusted according to the thickness of paper inserted therebetween, and a fusing roller gap adjusting method thereof.
2. Description of the Related Art
In printing apparatuses, a transfer roller transfers an image from a photoreceptor web onto a sheet of recording medium. A fusing roller forms a nip with the transfer roller and is often diametrically opposite the photoreceptor web as a sheet of recording medium passes between the transfer roller and the fusing roller. If the sheet of recording medium is thin or of standard thickness, the image successfully transfers onto the sheet of recording medium. However, if the sheet of recording medium is unusually thick, the image transfer is poor as the gap is too small between the transfer roller and the fusing roller.
What is needed is a printing apparatus that can adjust the size of the gap between the transfer roller and the fusing roller automatically based on the thickness of each sheet of recording medium so that unusually thick sheets, as well as thin or standard thickness sheets, can obtain a good image quality.
It is therefore an object of the present invention to provide an image forming apparatus where the gap between the fusing roller and the transfer roller can automatically be adjusted based on the thickness of the recording medium.
It is also an object to provide an image forming apparatus that can print high quality images on thin or standard thickness recording medium as well as on unusually thick sheets of recording medium.
It is further an object to provide an image forming apparatus that can measure the thickness of the sheet of recording medium prior to when said sheet of recording medium reaches the transfer roller and the fusing roller.
It is yet another object to provide an apparatus that can measure the thickness of a sheet of recording medium prior to when said sheet of recording medium reaches the transfer roller/fusing roller combination.
It is still another object to provide a mechanism for adjusting the gap between the transfer roller and the fusing roller by moving the fusing roller towards or away from the transfer roller prior to printing on a sheet of recording medium.
It is further an object of the present invention to provide a method for measuring a thickness of a sheet of recording medium, and based on said measurement, adjust the gap between the transfer roller and the fusing roller to provide optimum image quality on said sheet of recording medium.
Accordingly, to achieve the above object, there is provided a printer comprising a printing portion for forming a toner image on a circulating photoreceptor web, a transfer roller rotating in contact with the photoreceptor web so that the toner image formed on the photoreceptor web is transferred, a fusing roller installed to face the transfer roller, conveying rollers installed along a paper conveying path from a paper feeding portion to the transfer roller and the fusing roller, to be capable of being released corresponding to the thickness of the paper passing between the transfer roller and the fusing roller, a fusing roller gap adjusting portion for adjusting a separation distance of the fusing roller with respect to the transfer roller, a displacement measuring sensor installed to face the conveying roller for measuring a vertical displacement of the conveying roller varying according to the thickness of the paper passing the conveying roller, and a paper thickness calculating portion for calculating the thickness of the paper passing the conveying roller from the vertical displacement information output from the displacement measuring sensor and controlling the fusing roller gap adjusting portion so that a separation distance set to correspond to the calculated paper thickness is maintained between the transfer roller and the fusing roller.
It is preferred in the present invention that a surface of the conveying roller is formed of metal, the displacement measuring sensor is an electromagnetic induction sensor for forming an electromagnetic field with respect to the conveying roller and outputting an electric signal induced corresponding to the displacement of the conveying roller, and the paper thickness calculating portion calculates the thickness of the paper passing the conveying roller from the electric signal output from the electromagnetic induction sensor corresponding to the vertical displacement of the conveying roller.
Also, to achieve the above object, there is provided a fusing roller gap adjusting method of a printer comprising the steps of (A) calculating a reference position value of the conveying roller from the signal output from the displacement measuring sensor before the paper enters the conveying roller, (B) calculating the thickness of the paper by subtracting the reference position value from the vertical displacement value calculated from the value output from the displacement measuring sensor corresponding to the vertical displacement of the conveying roller when the paper passes the conveying roller, and (C) adjusting the position of the fusing roller so that a gap is set to correspond to the calculated paper thickness value is maintained between the transfer roller and the fusing roller.
It is preferred in the present invention that, in step (A), the reference position value is determined by averaging displacement values calculated from the values output from the displacement measuring sensor while rotating the conveying roller at least one time.
Also, it is preferred in the present invention that, in step (A), the maximum value of displacement values calculated from the values output from the displacement measuring sensor while rotating the conveying roller at least one time is determined as the reference position value.